A number of watercraft make use of fins that project from the water-facing surface of the craft. On planing craft, such as surfboards, the fins are typically foil-shaped to enhance the directional stability of the craft during high speed planing motion and to facilitate turning.
On watercraft such as surfboards the use of removable fins has become quite commonplace. These fins are removably and interchangeably fitted to the watercraft by means of fin mounting systems embedded in the water-facing surface of the craft, the fin mountings typically having a cavity that is configured to receive the base of the fin. Various securement mechanisms are used to secure the fin base in the mounting system cavity.
In conventional surfboard manufacturing terminology, the fin mounting systems are referred to as fin plugs.
One of the problems encountered with known fin plugs arises from the characteristics of surfboard construction. Surfboards are typically constructed from a relatively low-density foam core enveloped in a glass reinforced polyester resin skin laminated to the core. It will be appreciated that considerable torsional loads are imposed on the fin plug as a result of sideways thrust forces applied to the fin during use of the surfboard. In typical installations, the outer laminate of the surfboard is extended partially over the fin plug, but given the size limitations imposed by the locations where the fin plugs are installed on the surfboard, the laminate contact surface offered by the fin plug is generally insufficient to provide any real support to the fin plug in resisting the torsional loads imposed on the fin plug. The fin plug extends into the foam core of the surfboard and the fin plug is generally attached to the foam core by means of a suitable bonding agent, typically polyester resin which is conventionally used to laminate the surfboard. However, the low-density foam of the core generally does not have sufficient strength to resist the torsional fin plug loads without deformation or weakening of the surrounding foam over time, with consequential reduction in performance of the fin, cracking and shattering of the laminate in the vicinity of the fin plug and eventually delamination of the laminate from the core.
To overcome these problems, fin systems have been proposed that utilise a fin plug with a collar or flange extending about the open end of the fin-receiving cavity. The collar or flange upper surface is intended to stiffen the fin plug against side loads and to provide a bonding surface for the fibreglass laminate covering the fin plug. These fin plugs are typically of injection mouldable plastics, which generally does not bond well to the polyester resin most commonly used to laminate modern watercraft, unless the fin plug is treated, for instance by sanding, to provide some form of mechanical key and even this does little to improve bonding of the plastic to the resin. In addition, it will be appreciated that this introduces a secondary process that increases the cost and complexity of fin system installation.
It is an object of this invention to address these concerns.
The invention will be described with reference to surfboards as examples of watercraft, but it will be appreciated that the invention will find application in any watercraft that makes use of removable, replaceable fins that are mounted in a fin mounting assembly secured within a cavity formed in the water-facing surface of the craft.
Also, the fin mounting assembly is described and referred to as an assembly including a fin plug. In the majority of the examples described herein, the fin plug assembly is a typical surfboard fin plug assembly, but this is not intended to restrict the invention to surfboards and in this regard, the terms “fin plug” and “fin plug assembly” must be given a wider interpretation so as not to restrict the invention to surfboard fin plugs and fin plug assemblies or to the fin plug assembly illustrated in the drawings.